1. Field of the Invention
The present invention relates to a substrate for a magnetic recording medium improved by means of a chemical texture method and a process of producing the same.
2. Discussion of Background
Japanese Unexamined Patent Publication No. 165025/1989 discloses a chemical texture method (CTX method) as a method for forming a minute concavo-convex rough surface (texture) on a substrate for a magnetic recording medium. The CTX method is a method for remarkably improving not only magnetic properties of a magnetic film but also tribological properties of a substrate such as CSS properties and adsorption properties of a magnetic head onto a magnetic recording medium, which comprises (a) forming an alumite layer 3 having innumerable pores 2 on the surface by anodizing an aluminum or aluminium alloy substrate 1, (b) packing a material 4 having an etching rate different from the alumite into the pores of the alumite layer, (c) polishing the resultant substrate, (d) etching the polished substrate to form a minute concavo-convex pattern 4P on the alumite surface due to the above etching rate difference, and (e) forming a magnetic layer 5 and a protective layer 6 on the above treated surface, for example, by sputtering method, as shown in FIG. 4.
According to the above CTX method, since there are no protrusions protruded above the predetermined standard level, there are few head hits resulting in head crush and there is no fear that the protective layer 6 is cut by banishing step, thus providing a magnetic disk substrate having satisfactory CSS properties and corrosion resistance. The distance between pores 2 can be optionally adjusted, for example within a range of from 10 to 200 nm, by controlling anodizing voltage.
Recently, a high density magnetic recording medium using a Co-Pt type alloy as a magnetic layer has come to public notice. It is preferable for improving C/N properties to form the magnetic layer of this alloy in the vicinity of room temperature under a gas pressure range as high as possible (at least 10 mTorr). A graphite film containing diamond-like carbon used as a protective layer for this magnetic layer must be formed at a temperature as high as possible and under a pressure range as low as possible (lower than 5 mTorr). Otherwise, a protective layer having a satisfactory mechanical strength can not be formed but a soft carbon film rich in graphite structure is formed.
On the other hand, the texture obtained by the above known CTX method is too minute to the above-mentioned soft carbon film and the soft carbon film is worn when a magnetic head is in contact therewith during using the disk, thereby the concave part (valley) of the disk surface is rapidly buried with the worn carbon particles. Consequently, the area of the disk surface in contact with the magnetic head is increased, and accordingly the friction coefficient is enhanced, which results in poor CSS properties.
In order to solve the above-mentioned problems, it has been tried to reduce the packing rate of the electrolytic deposits into pores, but a satisfactory result has not been obtained.